The invention relates, generally, to a device for balancing second order vibrations of a rotating shaft and, more particularly, to an improved balancer for the crankshaft of a four cylinder in line engine for application in a motor vehicle.
Four cylinder in-line engines have become very popular in recent years, due, in large part, to their fuel economy. In addition to the engines efficiency, the four cylinder in line engine is a simple, low weight, compact design that exhibits superior torque characteristics.
While the engine's popularity has risen because of the aforementioned characteristics, the engine also exhibits undesirable second order vibrations. As is well known in the art, these second order vibrations are due to the fact that the piston rods are of finite length such that the motion of the pistons deviate from pure sinusoidal motion. The resulting imbalance cannot be compensated for by optimal dimensioning as is done with six cylinder engines. Moreover, because the vibration cannot be completely isolated from the body, the vibration results in unacceptably high levels of noise and vibration in the vehicle.
Numerous attempts have been made to eliminate these vibrations. For example, a number of patents assigned to Mitsubishi (U.S. Pat. Nos. 3,995,610, 4,000,666, 4,028,963, 4,074,589, 4,095,579, and 4,125,036) disclose a pair of counter rotating shafts set off from the axis of rotation of the crankshaft and operatively connected thereto by a rotary transmission means such as a chain. German Pat. Nos. 331,328 and 392,149 also show counter rotating shafts having eccentric weights used to balance the Crankshaft A further method for eliminating the second order vibrations is disclosed in German Pat. No. 2,720,284 where the standard crankshaft is replaced by a cam arrangement.
While these balancers are capable of reducing the second order vibrations, a complex and difficult installation procedure is required to arrange these large rotating shafts within the engine block. As a result, the practical applications of the prior art devices are severely limited.